ELM327P - N/A - Datasheet.Live

ELM327

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OBD to RS232 Interpreter

Almost all new automobiles produced today are

required, by law, to provide an interface from which

test equipment can obtain diagnostic information.

The data transfer on these interfaces follow several

standards, none of which are directly compatible

with PCs or PDAs. The ELM327 is designed to act

as a bridge between these On-Board Diagnostics

(OBD) ports and standard PC RS232 ports.

The ELM327 builds on improved versions of our

proven ELM320, ELM322, and ELM323 interfaces

by adding four CAN protocols to them. The result is

an IC that can automatically sense and convert the

nine most common protocols in use today. There are

a number of other improvements as well - a high

speed RS232 option with data buffering, battery

voltage monitoring, and the ability to remember the

last used protocol, to name only a few.

The following is only a “Quick Summary” of the

ELM327. For Example Applications, and a more

detailed discussion of the many features, download

the full datasheet.

• Supports 9 OBDII protocols

• Automatically searches for a protocol

• Fully configurable with AT commands

• High and Medium speed RS232

• Voltage input for battery monitoring

• Low power CMOS design

• Diagnostic trouble code readers

• Automotive scan tools

• Teaching aids

Description

Applications

Block Diagram

Features

ELM327QSA

Connection Diagram

PDIP and SOIC

(top view)

OBD Tx LED

OBD Rx LED

RS232 Tx LED

RS232 Rx LED

CAN Rx

CAN Tx

ISO L

ISO K

VDD

RS232 Rx

RS232 Tx

Busy

RTS

MCLR

Memory

Baud Rate

LFmode

J1850 Volts

XT1

XT2

VSS

ISO In

PWM In

J1850 Bus+

VPW In

J1850 Bus-

Vmeasure

VSS

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XT1 XT2

Command

and

Protocol

Interpreter

RS232Tx

RS232Rx

LFmode

4.00 MHz

RS232

Interface

ISO 15765-4

CAN ISO 9141-2

ISO 14230-4 SAE J1850

PWM & VPW

A/D

Converter

Baud Rate

…

Memory

status LEDs OBD interfaces

Busy

MCLR Vmeasure

RTS

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Pin Descriptions

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Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be

given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information

described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these

products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or

systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve

reliability, function, or design.

MCLR (pin 1)

A logic low applied to this input will reset the IC. If

unused, this pin should be connected to a logic high

(VDD) level.

Vmeasure (pin 2)

This analog input is used to measure a 0 to 5V

signal that is applied to it. Care must be taken to

prevent the voltage from going outside of the supply

levels of the ELM327, or damage may occur.

J1850 Volts (pin 3)

This output can be used to control a voltage supply

for the J1850 Bus + output. The pin will output a

logic high level when a nominal 8V is required (for

J1850 VPW), and will output a low level when 5V is

needed (as for J1850 PWM applications). If this

switching capability is not required for your

application, this output can be left open-circuited.

J1850 Bus+ (pin 4)

This active high output is used drive the J1850 Bus +

Line to an active level. Note that this signal does not

have to be used for the Bus - Line (as was the case

for the ELM320), since a separate J1850 Bus - drive

output is provided on pin 14.

Memory (pin 5)

This input controls the default state of the memory

option. If this pin is at a high level during power-up or

reset, the memory function will is enabled by default.

If it is at a low level, then the default will be to have it

disabled. Memory can always be controlled with the

AT M1 and AT M0 commands at other times.

Baud Rate (pin 6)

This input controls the baud rate of the RS232

interface. If it is at a high level during power-up or

reset, the baud rate will be set to 38400. If at a low

level, the baud rate will be 9600.

LFmode (pin 7)

This input is used to select the default linefeed mode

to be used after a power-up or system reset. If it is at

a high level, then by default messages sent by the

ELM327 will be terminated with both a carriage

return and a linefeed character. If it is at a low level,

lines will be terminated by a carriage return only.

This behaviour can always be modified by issuing an

AT L1 or AT L0 command (see the section on AT

Commands).

VSS (pins 8 and 19)

Circuit common must be connected to these pins.

XT1 (pin 9) and XT2 (pin 10)

A 4.000 MHz oscillator crystal is connected between

these two pins. Loading capacitors as required by

the crystal (typically 27pF each) will also normally be

connected between each of these pins and circuit

common (Vss).

VPW In (pin 11)

This is the active high input for the J1850 VPW data

signal. When at rest (bus recessive) this pin should

be at a low logic level. This input has Schmitt trigger

waveshaping, so no special amplification is required.

ISO In (pin 12)

This is the active low input for the ISO 9141 and

ISO 14230 data signal. It is derived from the K Line,

and should be at a high logic level when at rest (bus

recessive). No special amplification is required, as

this input has Schmitt trigger waveshaping.

PWM In (pin 13)

This is the active low input for the J1850 PWM data

signal. It should normally be at a high level when at

rest (ie. bus recessive). This input has Schmitt

trigger waveshaping, so no special amplification is

required.

ELM327QSA

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ELM327

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ELM327QSA

Ordering Information

These integrated circuits are 28 pin devices, available in either the 300 mil plastic DIP format or in the 300 mil SOIC

surface mount type of package. To order, add the appropriate suffix to the part number:

300 mil 28 pin Plastic DIP..............................ELM327P 300 mil 28 pin SOIC....................................ELM327SM

J1850 Bus- (pin 14)

This active high output is used to drive the J1850

Bus - Line to an active (dominant) level for J1850

PWM applications. If unused, the output can be left

open-circuited.

RTS (pin 15)

This active low “Request To Send” input can be

used to interrupt processing in order to send a new

command. Normally high, the line is brought low for

attention, and should remain so until the Busy line

(pin 16) indicates that the ELM327 is no longer busy.

This input has Schmitt trigger waveshaping.

Busy (pin 16)

This active high output shows the current state of the

ELM327. If it is at a low level, the processor is ready

to receive ASCII commands and characters, but if it

is at a high level, commands are being processed.

RS232Tx (pin 17)

This is the RS232 data transmit output. The signal

level is compatible with most interface ICs (output is

normally high), and there is sufficient current drive to

allow interfacing using only a PNP transistor, if

desired.

RS232Rx (pin 18)

This is the RS232 receive data input. The signal

level is compatible with most interface ICs (the level

is normally high), but can be used with other

interfaces as well, since the input has Schmitt trigger

waveshaping.

VDD (pin 20)

This pin is the positive supply pin, and should always

be the most positive point in the circuit. Internal

circuitry connected to this pin is used to provide

power on reset of the microprocessor, so an external

reset signal is not required. Refer to the Electrical

Characteristics section for further information.

ISO K (pin 21) and ISO L (pin 22)

These are the active high output signals which are

used to drive the ISO 9141 and ISO 14230 buses to

an active (dominant) level. Many new vehicles do not

require the L Line - if yours does not, you can simply

leave pin 22 open-circuited.

CAN Tx (pin 23) and CAN Rx (pin 24)

These are the two CAN interface signals that must

be connected to a CAN transeiver IC for proper

operation. If you are connecting to an existing CAN

system, the integrity of that sysem might be

jeopardized if a proper interface is not used. See the

Example Applications section for more information.

RS232 Rx LED (pin 25), RS232 Tx LED (pin 26),

OBD Rx LED (pin 27) and OBD Tx LED (pin 28)

These four output pins are normally high, and are

driven to low levels when the ELM327 is transmitting

or receiving data. Current capability is suitable for

directly driving most LEDs through current limiting

resistors, or interfacing to other logic for status

reporting. If unused, these pins should be left open-

circuited.

Pin Descriptions (continued)

Electrical Characteristics

Absolute Maximum Ratings

Storage Temperature.......................-65°C to +150°C

Ambient Temperature with

Power Applied....................................-40°C to +85°C

Voltage on VDD with respect to VSS............0 to +7.5V

Voltage on any other pin with

respect to VSS........................... -0.3V to (VDD + 0.3V)

Note:

Stresses beyond those listed here will likely damage

the device. These values are given as a design

guideline only. The ability to operate to these levels

is neither inferred nor recommended.

Notes: 1. This integrated circuit is produced with a Microchip Technology Inc.’s PIC18F248 or PIC18F2480 as the

core embedded microcontroller. For further device specifications, and possibly clarification of those given,

please refer to the appropriate Microchip documentation (available at http://www.microchip.com/).

2. This spec must be met in order to ensure that a correct power on reset occurs. It is quite easily achieved

using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as

may be obtained through direct connection to solar cells, or some charge pump circuits.

3. Device only. Does not include any load currents.

4. Pins 1, 11, 12, 13, 15 and 18 have internal Schmitt trigger waveshaping circuitry

5. The typical width of the Busy output pulse while the ELM327 interprets the command, measures the voltage,

scales it and transmits the result of a mid-range measurement at 38400 baud.

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ELM327

ELM327QSA Elm Electronics – Circuits for the Hobbyist

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All values are for operation at 25°C and a 5V supply, unless otherwise noted. For further information, refer to note 1 below.

Characteristic Minimum Typical Maximum ConditionsUnits

Supply voltage, VDD 4.5 5.0 5.5 V

VDD rate of rise 0.05 V/ms

Average supply current, IDD 9 mA

Input threshold voltage 1.0 1.3 V

Output low voltage

Output high voltage

current (sink) = 10 mA

current (source) = 10 mA

see note 2

see note 5

see note 3

Schmitt trigger

input thresholds

Brown-out reset voltage 4.07 4.2 4.59 V

rising

falling

A/D conversion time 7 msec

all except Schmitt inputs

0.3

4.6

3.0

1.4

see note 4

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ELM327

ELM327QSA Elm Electronics – Circuits for the Hobbyist

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AT Command Summary

General Commands

Dset all to Defaults

E0 Echo Off

E1 Echo On

Iprint the ID

L0 Linefeeds Off (default set by pin 7)

L1 Linefeeds On

WS Warm Start (quick software restart)

Zreset all

OBD Commands

AL Allow Long (>7 byte) messages

BD perform a Buffer Dump

BI Bypass the Initialization sequence

DP Describe the current Protocol

DPN Describe the Protocol by Number

H0 Headers Off (default)

H1 Headers On

M0 Memory Off (default set by pin 5)

M1 Memory On

MA Monitor All

MR hh Monitor for Receiver = hh

MT hh Monitor for Transmitter = hh

NL Normal Length (7 byte) messages

PC Protocol Close

R0 Responses Off

R1 Responses On

SH yzz Set Header

SH xx yy zz Set Header

SP h Set Protocol to h and save it

SP Ah Set Protocol to Auto, h and save it

ST hh Set Timeout to hh x 4 msec

TP h Try Protocol h

TP Ah Try Protocol h with Auto search

CAN Specific Commands

CAF1 CAN Automatic Formatting On

CAF0 CAN Automatic Formatting Off

CF hhh set the ID Filter to hhh

CF hh hh hh hh set the ID Filter to hhhhhhhh

CFC1 CAN Flow Control On

CFC0 CAN Flow Control Off

CM hhh set the ID Mask to hhh

CM hh hh hh hh set the ID Mask to hhhhhhhh

CP hh set CAN Priority (only for 29 bit)

CS show the CAN Status

ISO Specific Commands

IB 10 set the ISO Baud rate to 10400

IB 96 set the ISO Baud rate to 9600

SW hh Set Wakeup interval to hh x 20 msec

WM xx yy zz aa set the Wakeup Message

WM xx yy zz aa bb “ “

WM xx yy zz aa bb cc “ “

Misc. Commands

CV dddd Calibrate the Voltage to dd.dd volts

RV Read the Voltage